Modern automobiles regularly employ hydraulic braking systems. In this system the pressure applied to the brake pedal displaces a piston in a pressurized fluid chamber or master brake cylinder. In a dual circuit braking system pressure is generally applied to two braking systems via a tandem master cylinder, comprising two pressure chambers coupled, in series, by a secondary piston. A braking force amplifier may be incorporated into the master brake cylinder generating additional force proportional to the actuation of the brake pedal acting in the direction of actuation. The master brake cylinder is generally coupled to one or more wheel brake cylinders via hydraulic lines. The subsequent displacement of brake fluid transmits the pressure from brake pedal actuation to the brake linings, or brake shoes, forcing them into contact with the brake drum or brake disk. Deceleration is then achieved by the frictional force of the brakes acting against the rotation of the wheel. This direct coupling enables the braking force to be metered by the actuation of the brake pedal.
The sensitivity of the braking force to braking pedal actuation is influenced by the available actuation distance of the brake pedal. This distance is constrained by the installation space provided for the brake pedal and master brake cylinder dimensions. It is further limited by the operability of the brake pedal and the ease in which the motorist can negotiate between acceleration pedal and brake pedal. Finally, it is constrained by the motorist's ability to apply sufficiently high force throughout the total actuation distance of the brake pedal.
Brake pedals can therefore reach their physical travel limits by hitting the vehicle floor pan, or the master cylinder hits its end stop, preventing further pressure build up in the braking system, limiting the rate of vehicle deceleration. This is compounded when gas bubbles are present in the braking system increasing the brake pedal travel required for the brake linings to come into contact with the brake disk or brake drum.
The inventors recognized this design constriction and created a hydraulic brake system and operating method to reduce the effects of the physical limitations of the braking system. In one example, a method comprises generating braking pressure within the master cylinder of a hydraulic braking system via brake pedal actuation; and generating additional pressure within the master brake cylinder or in addition to the master brake cylinder in response to brake pedal actuation distance via an additional pressure generating device. In this way, it is possible to increase the braking force while reducing interference from the floor.
In another example, a system applies a resistive brake pedal pressure in response to a decrease of the residual actuation travel of the brake pedal and/or master brake cylinder and a corresponding increase in pressure delivered by the master brake cylinder. The “residual actuation travel distance” of the brake pedal is the remaining actuation distance available to the brake pedal before coming to a stop due to contact with the vehicle floor panel or the master brake cylinder hits its end stop. A minimal actuation distance can be a predetermined residual actuation distance. This is a predetermined brake pedal position and remaining travel or angle threshold. Brake pedal position can be monitored by sensors in the master brake cylinder determining brake pedal displacement from a no-load position and/or remaining available displacement distance. Sensors can also be incorporated into the brake pedal to determine pedal angle, displacement and/or remaining available travel. This may be utilized to continuously compare the prevailing residual actuation travel distance with the minimum residual actuation distance thus providing the ability to monitor both linear and angular actuation travel distance.
The minimum residual travel position can be used as a threshold to activate or regulate the resistive pressure applied against actuation of the brake pedal or the master braking cylinder and the corresponding increase in pressure delivered by the master brake cylinder. The pressure generating device may provide additional pressure to the master brake cylinder or in addition to the master brake cylinder. The pressure generating device can, in particular, be embodied as a pump or pressure reservoir connected to the master brake cylinder and/or the brake circuits. The device may also be connected to one or more brake circuit for activation purposes. The additional brake pressure in the master brake cylinder or in addition to the master brake cylinder is transmitted to one or more wheel brake devices generating additional braking force. The additional braking force creates a corresponding counter force exerted by way of the piston to the brake pedal resisting the further travel of the brake pedal. By virtue, the increased resistive force can provide an increase to the total force available for transmission to the braking system before the pedal and/or master braking cylinder meets its physical limits while preserving the required travel distance. As a consequence, a reduction in brake travel distance can be achieved and the effect of gas bubbles in the braking system can be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.